The chemical reactivity of aldehydes in general, and formaldehyde in particular, provides a wide variety of methods for their detection. However, many of these methods are not specific for formaldehyde, and some are not even specific for aldehydes in general. The use of Schiff's reagent for the detection of small quantities of formaldehyde has been widely used because it is both extremely simple and fairly sensitive. It is based on Denige's discovery that Schiff's fuchsin-bisulfite reagent gives a specific coloration with formaldehyde when employed in the presence of strong acids. A typical formulation for a modern version of Schiff's reagent involves a combination of sulphur dioxide and fuchsin (para-rosaniline hydrochloride). The sulphur dioxide is typically generated by mixing sodium bisulfite (NaHSO.sub.3) with hydrochloric acid. A typical formulation is as follows:
Dissolve 0.2 g of pure para-rosaniline hydrochloride in 120 ml of hot water. Cool and dissolve 2 g of anhydrous sodium bisulfite, followed by 2 ml of concentrated hydrochloric acid. Dilute the solution to 200 ml with water and store in well-filled amber bottles. The reagent is ready for use after standing at room temperature for about one hour. To employ the test, add 1 ml of concentrated sulphuric acid to 5 ml of the solution to be tested. Cool to room temperature and add 5 ml of the Schiff's reagent. The presence of formaldehyde is indicated by the development of a blue-violet color after 10 to 15 minutes.
Typical formulations in test procedures are taught by J. S. Swinehart, ORGANIC CHEMISTRY: AN EXPERIMENTAL APPROACH, Prentice-Hall, Inc. (1969), pages 423-424; J. F. Walker, FORMALDEHYDE, Third Edition, Rinehold Publishing Corporation, pages 467-469; S. Patai, THE CHEMISTRY OF THE CARBONYL GROUP, Interscience Publishers (1966), pages 381-382; and R. L. Shriner, THE SYSTEMIC IDENTIFICATION OF ORGANIC COMPOUNDS, John Wiley and Sons, Inc., Fifth Edition, pages 129-130. H. Puchtler, ON THE BINDING OF SCHIFF'S REAGENT AND THE PAS REACTION, HISTOCHEMISTRY 40, 291-299 (1974), discusses the Schiff's reaction in studies using molecular models. R. W. Horobin, A MECHANISTIC STUDY OF HISTOCHEMICAL REACTIONS BETWEEN ALDEHYDES AND BASIC FUCHSIN IN ACID ALCOHOL USED AS A SIMPLIFIED SUBSTITUTE FOR SCHIFF'S REAGENT, HISTOCHEMICAL JOURNAL 3 (1971) at 371-378, discusses the use of fuchsin in combination with an acid and an alcohol as a substitute for a conventional Schiff's reagent. H. Puchtler, ON THE HISTORY OF BASIC FUCHSIN ON ALDEHYDE-SCHIFF'S REACTIONS FROM 1862 to 1935, HISTOCHEMISTRY 41, 185- 194 (1975), discusses the history of reactions employing fuchsin.
Despite the extensive use which has been made of Schiff's reagents for detection of formaldehyde, there is a need for improvements. Specifically, even the best Schiff's reagent formulations tend to take a long time for the color change (i.e., from 10 to 15 minutes), and have a fairly high lower level detection limit (i.e., about 10 mg/L for formaldehyde and about 20 mg/L for gluteraldyhyude). In many fields, including hemodialysis, in which the equipment is sterilized with formaldehyde and then must be thoroughly rinsed and checked for the presence of residual formaldehyde, it would be very desirable to have an improved Schiff's reagent test which would indicate the presence of formaldehyde in a shorter time, and at lower concentrations than is presently possible.